Jørgen Gjernes Isaksen

Determination of Wall Tension in Cerebral Artery Aneurysms by Numerical Simulation

Background and Purpose— Cerebral artery aneurysms rupture when wall tension exceeds the strength of the wall tissue. At present, risk-assessment of unruptured aneurysms does not include evaluation of the lesions shape, yet clinical experience suggests that this is of importance. We aimed to develop a computational model for simulation of fluid-structure interaction in cerebral aneurysms based on patient specific lesion geometry, with special emphasis on wall tension. Methods— An advanced isogeometric fluid-structure analysis model incorporating flexible aneurysm wall based on patient specific computed tomography angiogram images was developed. Variables used in the simulation model were retrieved from a literature review. Results— The simulation results exposed areas of high wall tension and wall displacement located where aneurysms usually rupture. Conclusion— We suggest that analyzing wall tension and wall displacement in cerebral aneurysms by numeric simulation could be developed into a novel method for individualized prediction of rupture risk.

Computation of Hemodynamics in the Circle of Willis

Background and Purpose— Wall shear stress (WSS) and pressure are important factors in the development of cerebral aneurysms. We aimed to develop a computational fluid dynamics simulator for flow in the complete circle of Willis to study the impact of variations in vessel radii and bifurcation angles on WSS and pressure on vessel walls. Methods— Blood flow was modeled with Navier-Stokes equations as an incompressible newtonian fluid within rigid vessel walls. A model of the circle of Willis geometry was approximated as a network of tubes around cubic curves. Pulsatile inlet flow rates and constant outlet pressure were used as boundary conditions. Results— The simulations confirmed that differences in vessel radii and asymmetric branch angles influence WSS magnitude and spatial distribution. High WSS occurred at locations where aneurysms are frequent and in anatomic variants known to be associated with an increased risk for aneurysm development. Conclusions— Computational fluid dynamics analysis can be applied to the complete circle of Willis and should be used to study the pathophysiology of this complex vascular structure, including risk factors for aneurysm development. Further development of the method should include simulations with flexible vessel walls.

Risk factors for aneurysmal subarachnoid haemorrhage: the Tromsø study

Objectives: To conduct a population based case-control study with premorbid registration of potential risk factors to address the difficulty in identifying risk factors for aneurysmal subarachnoid haemorrhage (SAH). SAH is rare in prospective studies, and retrospective studies may have a selection bias. Methods: The Tromsø health study is a population based survey of risk factors for cardiovascular disease in 27 161 subjects. 26 cases of aneurysmal SAH were identified in which risk factors were registered before the bleeding. Four age and sex matched controls were selected for each case. A backward logistic regression analysis was conducted and odds ratios (ORs) for significant risk factors were calculated. Systolic and diastolic blood pressure, cigarette smoking habits, serum concentrations of lipoproteins, body mass index, and coffee consumption were analysed. Results: The crude annual incidence rate of aneurysmal SAH was 8.84/100 000 population. The proportion of current smokers was significantly (p = 0.003) higher in patients with SAH (73.1%) than in controls (41.3%). Drinking more than five cups of coffee per day was more common among patients (85%) than controls (59%) (p = 0.004). Mean (SD) systolic blood pressure was higher (p = 0.017) in patients (154.0 (32.5)) than in controls (136.3 (23.3)). Regression analysis showed that cigarette smoking (p = 0.04), systolic blood pressure (p < 0.0001), and coffee consumption (p = 0.004) were independent risk factors for SAH. The OR of current smokers versus never smokers was 4.55 (95% confidence interval (CI) 1.08 to 19.30) and the OR of drinking more than five cups of coffee a day was 3.86 (95% CI 1.01 to 14.73). The OR of an increase in systolic blood pressure of 20 mm Hg was 2.46 (95% CI 1.52 to 3.97). Conclusions: Cigarette smoking and hypertension are significant independent risk factors for aneurysmal SAH. A high coffee consumption may also predispose patients to aneurysmal SAH.

Predictors for cognitive impairment one year after surgery for aneurysmal subarachnoid hemorrhage

ObjectiveTo assess predictors for cognitive impairment one year after spontaneous subarachnoid hemorrhage (SAH). Evaluated predictors were the total amount of cisternal blood seen on computed tomography (CT) in the acute phase as measured by the Fisher grade, neurological grade at admission classified according to the Hunt and Hess scale, aneurysm site and patient’s age, gender and education level.Method44 patients were operated by surgical clipping within 72 hours after CT verified aneurysmal SAH. After twelve months the remaining 42 patients were assessed by neuropsychological test, Beck Depression Inventory (BDI), the Glasgow Outcome Scale (GOS) and CT. Multiple regression analysis was conducted where predictor variables were independent factors and a global impairment index calculated for each patient was the dependent factor.ResultsThe Fisher grade was the only independent predictor for neuropsychological impairment. Most patients had good neurological outcome as measured by the GOS and at the same time suffered from some degree of cognitive impairment at follow-up. Individual analysis of cognitive test scores showed mild to moderate dysfunction across multiple cognitive domains. Most frequent impairments were found in domains of memory, executive function and speed of information processing. Age below 50 years was associated with relatively better outcome.ConclusionThe severity of cognitive impairment one year post SAH is predicted by the volume of blood in the subarachnoid space as measured by the Fisher score.

Cerebral aneurysm morphology before and after rupture: nation-wide case series of 29 aneurysms

Background and Purpose— Using postrupture morphology to predict rupture risk of an intracranial aneurysm may be inaccurate because of possible morphological changes at or around the time of rupture. The present study aims at comparing morphology from angiograms obtained prior to and just after rupture and to evaluate whether postrupture morphology is an adequate surrogate for rupture risk. Methods— Case series of 29 aneurysms from a nationwide retrospective data collection. Two neuroradiologists who were blinded to pre- versus postrupture images assessed predefined morphological parameters independently and reached consensus regarding all measurements. Prerupture morphology and respective changes after rupture were quantified and linked to risk factors and to the risk of rupture according to the PHASES (population, hypertension, age, size of aneurysm, earlier subarachnoid hemorrhage from another aneurysm, site of aneurysm) and unruptured intracranial aneurysm treatment (UIAT) scores. Results— All 1-dimensional parameter medians were significantly larger after rupture, except neck diameter. Number of aneurysms with daughter sacs was 9 (31%) before and 17 (59%) after rupture (P=0.005). Aneurysm growth from the images prior to and just after rupture increased with the time elapsed between images. Aneurysms in patients with hypertension were significantly larger at diagnosis. Prerupture morphology did not differ in relation to smoke status. Clinical risk factors were not significantly associated with morphological change. Conclusions— The changes in aneurysm morphology observed after rupture reflect the compound effect of time with successive growth and formation of irregularities and the impact of rupture per se. Postrupture morphology should not be considered an adequate surrogate for the prerupture morphology in the evaluation of rupture risk.

Results of surgery for aneurysmal subarachnoid haemorrhage in northern Norway: a retrospective study with special focus on timing of surgery in a rural area.

Egge A, Romner B, Waterloo K, Isaksen J, Kloster R, Ingebrigtsen T, Trumpy JH. Results of surgery for aneurysmal subarachnoid haemorrhage in northern Norway: a retrospective study with special focus on timing of surgery in a rural area. Acta Neurol Scand 2002: 106: 355–360.

Introduction of Endovascular Embolization for Intracranial Aneurysms in a Low-volume Institution

Background: Studies indicate a relationship between hospital caseload and health outcomes after both surgical and endovascular repair of intracranial aneurysms. Purpose: To evaluate outcomes after introduction of endovascular embolization for intracranial aneurysms in a low-volume regional university hospital. Material and Methods: Retrospective study of 243 consecutive patients treated for 284 intracranial aneurysms with endovascular embolization or surgical clipping from 2000 to 2006 at the University Hospital of North Norway. Postoperative complications were registered. The Glasgow Outcome Scale (GOS) was used for assessment of outcome. Results: The mean annual number of procedures was 39 (microsurgery 23, embolization 16). Seventy-four percent of patients with ruptured aneurysms and all patients with unruptured aneurysms had a favorable outcome (GOS 4 or 5) at 1 year follow-up. Patients with subarachnoid hemorrhage were more likely to experience postoperative complications than patients treated for unruptured aneurysms (42% versus 8% of the patients, P<0.01). The immediate incomplete occlusion rate (Raymond II–III) in the initial embolization procedure was 29%. Ten endovascularly treated patients and one surgically treated patient required retreatments due to residual aneurysm or neck remnants. Conclusion: The present study indicates that acceptable outcome from aneurysm treatment, both endovascular and microsurgical, is possible in a low-volume institution.

High-Fidelity Finite Element Mesh Generation for Fluid-Structure Interaction Analysis of Cerebral Aneurysms

Nowadays approximately 3–6% of the population is estimated to have unruptured cerebral aneurysms. The rupture risk of aneurysms can be predicted by using computational tools and patient-specific models. As an ideal method, we can assess the risk factors by determining the blood tension and the material strength of the wall tissue in the aneurisms. Although it is hard to obtain aneurismal material strength without invasive measurement, it is possible to estimate the wall tension by numerical simulation [1].Copyright